A crimping method is widely used as a method for connecting a terminal and an electric wire. Crimping means a technique in which a conductor exposed portion of an electric wire is inserted into a conductor crimping portion and the electric wire is electrically connected to the conductor crimping portion by crimping the conductor crimping portion with a crimp tool or the like so as to embrace the conductor exposed portion therein. The conductor crimping portion has a substantially U-shape and is provided on a terminal.
In order to improve the connecting performance by crimping, it is conventionally practiced to plate a surface of a terminal with tin to thereby increase the crimping performance. In the event that the terminal plated with tin in the way described above is crimped to an electric wire, it is known that the tin with which the terminal is plated acts an intermediary between a conductor of the electric wire and a base material of the terminal to thereby improve the connecting performance. It is also known that by changing the thickness of tin applied to the terminal depending on the location on the terminal, the wear of crimping dies is reduced or a terminal inserting force applied when fitting an electric connecting portion on a mating terminal is attempted to be reduced (refer to Patent Document 1).
Incidentally, it is general practice to use a copper electric wire for a wiring harness which is disposed in an interior of a vehicle such as a motor vehicle. Conventionally, an aluminum electric wire has been little used since the aluminum electric wire which is inferior to the copper electric wire in physical properties such as conductivity and strength has been difficult to be used. In recent years, however, demands for use of aluminum electric wires have been enhanced in consideration of reduction in weight of the vehicle for improvement in fuel economy and recycling capability.
In the event of an aluminum electric wire being used, since aluminum or an aluminum alloy which makes up a conductor of the electric wire is inferior to copper in mechanical strength and electricity conductivity, a further increase in connecting performance at a conductor crimping portion is needed. In addition, since an oxide coating having a high intrinsic resistance value is normally produced on a surface of the conductor of aluminum or an aluminum alloy, a sufficient contact for electric continuity must be realized between conductors (that is, the terminal and the aluminum or aluminum alloy conductor) by breaking the oxide coating in crimping the terminal to the aluminum electric wire. However, since aluminum electric wires have been little used, no sufficient study has been made in that field under the current circumstances.    Patent Document 1: Japanese Patent Publication No. 11-121075